1. Field of the Invention
The present invention relates to a traverse linearity compensation method and a rotational accuracy compensation method of a measuring device. More specifically, it relates to a traverse linearity compensation method of a measuring device having a linear movement mechanism, such as a roundness-measuring device and a roughness-measuring device, for compensating traverse linearity of the linear movement mechanism. It also relates to a rotational accuracy compensation method of a measuring device having a rotary mechanism such as a roundness-measuring device for compensating a rotational accuracy of the rotation mechanism.
2. Description of Related Art
When a workpiece is measured by a measuring device having a linear movement mechanism as a guide (reference) such as a roundness-measuring device and a roughness-measuring device, the resulted measurement data is a composition of a profile data of the workpiece and a mechanical accuracy of the linear movement mechanism (traverse linearity).
Similarly, when a workpiece is measured by a measuring device having a rotary mechanism as a guide (reference) such as a roundness-measuring device, the resulted measurement data is a composition of a profile data of the workpiece and the mechanical accuracy of the rotary mechanism (rotational accuracy).
In order to obtain a correct workpiece profile against the mechanical accuracy of the linear movement mechanism and the rotary mechanism, the traverse linearity of the linear movement mechanism or the rotational accuracy of the rotary mechanism has to be separated and removed from the measurement data.
Conventionally, a xe2x80x9cstraightness measurable roundness-measuring devicexe2x80x9d, Japanese Patent No. 2935603, has been proposed for separating and removing the traverse linearity of the linear movement mechanism from the measurement data.
The device has a rotary table for mounting a traverse linearity check gauge, a sensor for detecting a surface position of a side of the traverse linearity check gauge, a column for movably holding the sensor along the surface of the traverse linearity check gauge, a first storing means for storing data obtained by the sensor as a first data, a second storing means for storing data as a second data obtained by rotating the traverse linearity check gauge around a rotational axis of the rotary table by 180 degrees and by sensing the surface position of the same side of the traverse linearity check gauge, and a processor for calculating a linearity error compensation amount of the column based on the first data and the second data.
Since the above-described xe2x80x9cstraightness measurable roundness-measuring devicexe2x80x9d, Japanese Patent No. 2935603 employs so-called reversal method, which requires an initial measurement (the first measurement) and the second measurement conducted after rotating the rotary table by 180 degrees, and where the measurement locus has to be identical on the target workpiece surface, following problems accompanied.
It is extremely difficult to correctly set the workpiece during measurement and the setting requires skill. In addition, considerable number of steps, such as reversing the location of the sensor in conducting the two measurements is necessary therefor. Further, the guide of the sensor is not always in the regular condition (for instance, in the roundness measuring device, projection amount of an arm holding the sensor is not always the same), so that error is likely to be caused.
On the other hand, the following method is known for separating and removing the rotational accuracy of the rotary mechanism.
[Method 1] A spherical master workpiece having smooth surface, for instance, semispherical master workpiece (reference hemisphere) is measured and resulted measurement data is separated and removed from the workpiece measurement data as the rotational accuracy.
[Method 2] Phase difference method (multi step method), where measurement is conducted while shifting phase of a reference hemisphere by a predetermined pitch relative to a rotary table.
However, following problems occur in the above-described [method 1] and [method 2].
Since the reference hemisphere has its inherent profile error, reliability of [method 1] is not so high.
In [method 2], the reference hemisphere has to be measured while being shifted by a predetermined pitch relative to the rotary table. In order to shift the phase accurately, specially designed jig and skilled technique are required and a larger number of steps are required as the divisional number of the shift amount is increased.
An object of the present invention is to provide a traverse linearity compensation method capable of overcoming the above-described disadvantage of the reversal method and obtaining highly reliable measurement data without modifying existing devices.
A traverse linearity compensation method of a measuring device according to the present invention employs following arrangement for achieving the above object.
The present invention is a traverse linearity compensation method of a measuring device having a linear movement mechanism, the method including: a traverse linearity data calculating step for measuring a master workpiece of which profile data is value-specified in advance while moving a sensor by the linear movement mechanism of the measuring device and for subtracting the value-specified profile data from the master workpiece measurement data to obtain a traverse linearity data of the linear movement mechanism; a workpiece measurement data calculating step for measuring a workpiece while moving the sensor by the linear movement mechanism of the measuring device to obtain a measurement data of the workpiece; and a workpiece profile calculating step for subtracting the traverse linearity data from the workpiece measurement data to obtain a true value data of the workpiece.
According to the above arrangement, the master workpiece of which profile data is value-specified in advance is measured while moving the sensor by the linear movement mechanism of the measuring device the traverse linearity data of the linear movement mechanism is obtained by subtracting the previously measured profile data from the master workpiece measurement data during the traverse linearity data calculating step. Subsequently, during the workpiece profile calculating step, the workpiece is measured while moving the sensor by the linear movement mechanism of the measuring device to obtain the workpiece measurement data. During the workpiece profile calculating step, the true value data of the workpiece is obtained by subtracting the traverse linearity data from the workpiece measurement data.
Accordingly, since only one measurement is necessary during the traverse linearity data calculating step, the disadvantage of the reversal method can be solved. Further, since the sensor guide is not required to be the same, more accurate compensation result can be obtained. Further, since the compensation is conducted by processing the workpiece measurement data, highly reliable measurement data can be obtained without special arrangement for the measuring device. Further, since the calculation of the traverse linearity data and the compensation of the traverse linearity data to the workpiece measurement data can be conducted by an application program independent of the measuring device, the data can be more accurately compensated by conducting processing such as averaging processing of the master workpiece measurement data (processing for obtaining average value of a plurality of master workpiece measurement data obtained by repeatedly measuring the same position under the same condition) for reducing electric noise and dispersion of the measurement data according to measurement environment.
In a traverse linearity compensation method of a measuring device having a linear movement mechanism according to the present invention, the method may include: a traverse linearity data calculating step for measuring a master workpiece of which profile data is value-specified in advance while moving a sensor by the linear movement mechanism of the measuring device and for subtracting the value-specified profile data from the master workpiece measurement data to obtain a traverse linearity data of the linear movement mechanism; a traverse linearity data storing step for storing the traverse linearity data obtained in the traverse linearity data calculating step; a workpiece measurement data calculating step for measuring a workpiece while moving the sensor by the linear movement mechanism of the measuring device to obtain a measurement data of the workpiece; a workpiece measurement data storing step for storing the workpiece measurement data obtained in the workpiece measurement data storing step; and a workpiece profile calculating step for reading out the stored workpiece measurement data and the traverse linearity data stored in the respective storing steps and for subtracting the traverse linearity data from the workpiece measurement data to obtain a true value data of the workpiece.
According to the above arrangement, since the traverse linearity data storing step for storing the traverse linearity data and the workpiece measurement data storing step for storing the workpiece measurement data are added, the traverse linearity data and the workpiece measurement data can be acquired and stored at different time point and the true value data of the workpiece can be obtained by subtracting the traverse linearity data from the workpiece measurement data as desired (as necessary).
In the traverse linearity compensation method according to the present invention, a measurement jig having a mount provided with a workpiece mounting surface and an origin-setting reference ball buried in the mount or the master workpiece with a part thereof being exposed may preferably be used in the traverse linearity data calculating step, and, after a square-pillar master workpiece is rested on the workpiece mounting surface of the mount and a measurement origin is set by locating the sensor of the measuring device on a vertex of the reference ball, the sensor may be moved along a side of the master workpiece by the linear movement mechanism to measure the master workpiece.
According to the above arrangement, since the master workpiece is measured using the measurement jig having the mount and the origin-setting reference ball and, after the measurement origin is set by locating the sensor of the measuring device to the origin-setting reference ball, the master workpiece is measured while moving the sensor along the measurement surface of the master workpiece by the linear movement mechanism, the sensor can be accurately moved from the measurement origin to the designated measurement point of the master workpiece, so that the master workpiece can be measured highly accurately.
In the traverse linearity compensation method of a measuring device according to the present invention, the mount may preferably be formed in a half-cylinder having a vertical reference surface orthogonal with the workpiece mounting surface, the reference ball being buried on the vertical reference surface with a part thereof being exposed.
According to the above arrangement, in compensating the traverse linearity (traverse linearity of a column or slider for vertically moving the sensor) of a roundness measuring device, the mount is set on a rotary table so that the vertical reference surface of the mount is situated at the center of the rotary table of the roundness measuring device, and subsequently, after the master workpiece is rested on the workpiece mounting surface of the mount so that one side of the master workpiece coincides with the vertical reference surface of the mount, the probe of the sensor is brought into contact with the reference ball and the position of the sensor is adjusted in order that the probe captures the vertex of the reference ball both in vertical and in horizontal direction. After setting the measurement origin at the condition, the probe of the sensor is brought into contact with one point on the surface of the master workpiece a predetermined distance away from the measurement origin, and the sensor is moved upwardly (or downwardly), thus measuring the vertical traverse linearity of the master workpiece on the entire length.
Accordingly, since the master workpiece can be located on the rotary table using the measurement jig and the measurement origin can be set by bringing the probe of the sensor into contact with the reference ball, the probe of the sensor can be constantly located at a regular position of the master workpiece, so that the locus from the regular position on the master workpiece can be measured.
Another object of the present invention is to provide a rotational accuracy compensation method of a measuring device capable of overcoming the disadvantage of the above-described conventional measuring method, especially the phase-difference method, and obtaining highly reliable measurement data without modifying the existing device.
Accordingly, in order to attain the above object, the rotational accuracy compensation method according to the present invention employs following arrangement.
A rotational accuracy compensation method of a measuring device according to the present invention is a rotational accuracy compensation method of a measuring device having a rotary mechanism, the method including: a rotational accuracy data calculating step for measuring a profile of a master workpiece by a sensor while rotating a master workpiece of which profile data at a data acquisition position is value-specified in advance by a rotary mechanism of the measuring device and for subtracting the value-specified profile data from the master workpiece measurement data to obtain a rotational accuracy data of the rotary mechanism; a workpiece measurement data calculating step for measuring the profile of the workpiece by the sensor while rotating the workpiece by the rotary mechanism of the measuring device to obtain a measurement data of the workpiece; and a workpiece profile calculating step for subtracting the rotational accuracy data from the workpiece measurement data to obtain a true value data of the workpiece.
According to the above arrangement, while rotating the master workpiece of which profile data at the data acquisition position is value-specified by a rotary mechanism of the measuring device, the profile of the master workpiece at the data acquisition position is measured by the measuring device and the rotational accuracy data of the rotary mechanism is obtained by subtracting the value-specified profile data from the master workpiece measurement data during the rotational accuracy data calculating step. During the workpiece measurement data calculating step, the profile of the workpiece is measured by the sensor while rotating the workpiece by the rotary mechanism of the measuring device to obtain the measurement data of the workpiece. During the workpiece profile calculating step, the true value data of the workpiece is obtained by subtracting the rotational accuracy data from the workpiece measurement data.
Accordingly, since the master workpiece is not required to be shifted by a predetermined pitch relative to rotary table, the disadvantage of phase difference method, i.e. skilled work and numerous steps, can be eliminated. Further, since the compensation is conducted by processing the workpiece measurement data, highly reliable measurement data can be obtained without special arrangement for the measuring device. Further, since the calculation of the rotational accuracy data and the compensation of the rotational accuracy data to the workpiece measurement data can be conducted by an application program independent of the measuring device, the data can be more accurately compensated by conducting processing such as averaging processing of the master workpiece measurement data (processing for obtaining average value of a plurality of master workpiece measurement data obtained by repeatedly measuring the same position under the same condition) for reducing electric noise and dispersion of the measurement data according to measurement environment.
In the rotational accuracy compensation method of a measuring device according to the present invention, the method may include: a rotational accuracy data calculating step for measuring a profile of a master workpiece by a sensor while rotating a master workpiece of which profile data at a data acquisition position is value-specified in advance by a rotary mechanism of the measuring device and for subtracting the value-specified profile data from the master workpiece measurement data to obtain a rotational accuracy data of the rotary mechanism; a rotational accuracy data storing step for storing the rotational accuracy data obtained in the rotational accuracy data calculating step; a workpiece measurement data calculating step for measuring the profile of the workpiece by the sensor while rotating the workpiece by the rotary mechanism of the measuring device to obtain a measurement data of the workpiece; a workpiece measurement data storing step for storing the workpiece measurement data obtained in the workpiece measurement data calculating step; and a workpiece profile calculating step for reading out the workpiece measurement data and the rotational accuracy data stored in the respective storing steps and for subtracting the rotational accuracy data from the workpiece measurement data to obtain a true value data of the workpiece.
According to the above arrangement, since the rotational accuracy data storing step for storing the rotational accuracy data and the workpiece measurement data storing step for storing the workpiece measurement data are added, the rotational accuracy data and the workpiece measurement data can be separately acquired and stored at different time point and the true value data of the workpiece can be obtained by subtracting the rotational accuracy data from the workpiece measurement data as desired (as necessary).
In the rotational accuracy compensation method of the measuring device according to the present invention, a measurement jig provided with a cylindrical mount having a hemispherical master workpiece on an upper surface thereof and an origin-setting reference ball buried in the mount or the master workpiece with a part thereof being exposed may preferably be used, where, after a measurement origin is set by locating a sensor of the measuring device to a vertex of the reference ball, the sensor may preferably be located to the data acquisition position of the master workpiece and the master workpiece may preferably be measured while rotating the master workpiece by the rotary mechanism.
According to the above arrangement, the measurement jig having the mount on which the spherical master workpiece is provided and the origin-setting reference ball is used, where the measurement origin is set by locating the sensor of the measuring device to the origin-setting reference ball and, subsequently, the sensor is located to the data acquisition position of the master workpiece and the master workpiece is measured while rotating the master workpiece by the rotary mechanism. Therefore, the sensor can be accurately positioned to the data acquisition position of the workpiece, so that the master workpiece can be accurately measured.